Supporting Information

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1 Supporting Information Porous Nickel-Iron Selenide Nanosheets as Highly Efficient Electrocatalysts for Oxygen Evolution Reaction Zhaoyang Wang, Jiantao Li, Xiaocong Tian, Xuanpeng Wang, Yang Yu, Kwadwo Asare Owusu, Liang He, * Liqiang Mai * State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan , Hubei (P.R. China) mlq518@whut.edu.cn; hel@whut.edu.cn Fax: ; Tel: S-1

2 Figure S1. XRD pattern (a), SEM images (b, c), TEM image (d), SEM image and elemental mapping images (e) of the ultrathin Ni-based nanosheet precursor. Figure S2. XRD pattern (a), SEM images (b, c), TEM image (d), SEM image and elemental mapping images (e) of the ultrathin NiFe-based nanosheet precursor. S-2

3 Figure S3. XRD pattern (a), SEM images (b, c), elemental mapping images (d), EDS line scans (e), TEM image (f), and HRTEM image (g) of the porous NiSe 2 nanosheets. Figure S4. XRD patterns of the porous (Ni 0.75 Fe 0.25 )Se 2 nanosheets, and the porous NiSe 2 nanosheets. S-3

4 Figure S5. High-resolution SEM image (a), TEM image (b), and (c) HRTEM image of the porous (Ni 0.75 Fe 0.25 )Se 2 nanosheet. TEM image (d) of the porous NiSe 2 nanosheet. Figure S6. XRD pattern (a), Nitrogen adsorption-desorption isotherm (b), SEM images (c), HRTEM image and SAED pattern (d) of IrO 2 catalyst. S-4

5 Figure S7. Nitrogen adsorption-desorption isotherm of porous (Ni 0.75 Fe 0.25 )Se 2 nanosheets, NiFe-based nanosheet precursor, porous NiSe 2 nanosheets, and Ni-based nanosheet precursor. Table S1. ICP results of NiFe-based nanosheet precursor, porous (NiFe)Se nanosheets, and porous NiSe 2 nanosheets. S-5

6 Figure S8. High-resolution (a) Ni 2p, (b) Se 3d, and (c) O 1s XPS spectra for the porous NiSe 2 nanosheets. High-resolution (d) Ni 2p and (e) Fe 2p XPS spectra for the NiFe-based precursor. XPS survey spectrum for the (f) porous (Ni 0.75 Fe 0.25 )Se 2 nanosheets. Figure S9. The double-layer capacitance measurements of the obtained (Ni 0.75 Fe 0.25 )Se 2 (a), NiFe-based precursor (b), NiSe 2 (c), Ni-based precursor (d) and carbon fiber cloth (e) samples. The ECSA was determined by measuring the capacitive current associated with double-layer charging from the cyclic voltammetry (CV) curves at different scan rates. A linear slope is obtained from the plot of the differences in the charging current density (J a -J c ) at 0.2 V (vs. saturated calomel electrode) against the scan rate. The linear slope is twice of the double-layer capacitance (C dl ). The CV of the samples were tested using a three electrode system in a V potential window with the scan rates from 20 mv s -1 to 120 mv s -1. S-6

7 Figure S10. XPS spectra in the (a) Ni 2p, (b) Fe 2p, (c) Se 3d, and (d) O 1s regions for the (Ni 0.75 Fe 0.25 )Se 2 catalyst after OER electrolysis in 1 M KOH. XPS survey spectrum of the (e) post-oer (Ni 0.75 Fe 0.25 )Se 2 catalyst. Figure S11. XPS spectra in the (a) Ni 2p, (b) Se 3d, and (c) O 1s regions for the NiSe 2 catalyst after OER electrolysis in 1 M KOH. XPS survey spectrum of the (d) post-oer NiSe 2 catalyst. Table S2. ICP results for the porous (NiFe)Se nanosheets and porous NiSe 2 nanosheets after OER electrolysis. S-7

8 Table S3. The composition analysis from deconvolution of XPS spectra before and after OER test. Figure S12. XRD patterns of the (Ni 0.75 Fe 0.25 )Se 2 (a) and NiSe 2 (b) after OER electrolysis. Figure S13. SEM image (a) and EDS spectrum (b) for the (Ni 0.75 Fe 0.25 )Se 2 catalyst before OER electrolysis, SEM image (c) and EDS spectrum (d) for the (Ni 0.75 Fe 0.25 )Se 2 catalyst after OER electrolysis. S-8

9 Figure S14. Mass activity based on the weight of the (Ni 0.75 Fe 0.25 )Se 2, NiFe-based nanosheet precursor, NiSe 2, Ni-based nanosheet precursor, and IrO 2 catalysts at 1.6 V vs. reversible hydrogen electrode (RHE). Table S4. The R s and R ct values of the samples from EIS spectra (Figure 5) simulated using the corresponding equivalent circuit. S-9

10 Table S5. Comparison of OER activity for the (Ni 0.75 Fe 0.25 )Se 2 /CFC with some reported non-noble metal catalysts in alkaline electrolytes. Catalysts Mass loading mg cm -2 Current density (ma cm -2 ) Overpotential (mv) Tafel sloper (mv dec -1 ) Double layer capacitance (mfcm -2 ) Electrolyte Substrate Reference (Ni 0.75 Fe 0.25 )Se 2 nanosheets NiCo 2 S 4 nanowires M KOH Carbon cloth This work M KOH Carbon cloth (1) NiSe nanowires NA 1 M KOH Ni foam (2) Ni 3 N nanosheets NA 1 M KOH Carbon cloth (3) Co 4 N nanowires M KOH Carbon cloth (4) Co 3 O 4 /C nanowires CoP nanorods/c CoNi(OH) x nanotubes (Ni, Co) 0.85 Se nanotubes Zn x Co 3-x O 4 nanowires FeOOH/Co /FeOOH nanotubes M KOH Cu foil (5) NA 1 M KOH Glassy carbon (6) NA 1 M KOH Cu foil (7) M KOH Carbon cloth (8) M KOH Ti foil (9) M NaOH Ni foam (10) Additional references: (1) Liu, D.; Lu, Q.; Luo, Y.; Sun, X.; Asiric, A. M. NiCo 2 S 4 Nanowires Array as an Efficient Bifunctional Electrocatalyst for Full Water Splitting with Superior Activity. Nanoscale 2015, 7, (2) Tang, C.; Cheng, N.; Pu, Z.; Xing, W.; Sun, X. NiSe Nanowire Film Supported on Nickel Foam: An Efficient and Stable 3D Bifunctional Electrode for Full Water Splitting. Angew. Chem. Int. Ed. 2015, 54, (3) Xu, K.; Chen, P.; Li, X.; Tong, Y.; Ding, H.; Wu, X.; Chu, W.; Peng, Z.; Wu, C.; Xie, Y. Metallic Nickel Nitride Nanosheets Realizing Enhanced Electrochemical Water Oxidation. J. Am. Chem. Soc. 2015, 137, (4) Chen, P.; Xu, K.; Fang, Z.; Tong, Y.; Wu, J.; Lu, X.; Peng, X.; Ding, H.; Wu, C.; Xie, Y. Metallic Co 4 N Porous Nanowire Arrays Activated by Surface Oxidation as Electrocatalysts for the Oxygen Evolution Reaction. Angew. Chem. Int. Ed. 2015, 54, (5) Ma, T. Y.; Dai, S.; Jaroniec, M.; Qiao, S. Z. Metal-Organic Framework Derived Hybrid Co 3 O 4 -Carbon Porous Nanowire Arrays as Reversible Oxygen Evolution Electrodes. J. Am. Chem. Soc. 2014, 136, S-10

11 (6) Chang, J.; Xiao, Y.; Xiao, M.; Ge, J.; Liu, C.; Xing, W. Surface Oxidized Cobalt-Phosphide Nanorods as an Advanced Oxygen Evolution Catalyst in Alkaline Solution. ACS Catal. 2015, 5, (7) Li, S.; Wang, Y.; Peng, S.; Zhang, L.; Al-Enizi, A. M.; Zhang, H.; Sun, X.; Zheng, G. Co Ni Based Nanotubes/Nanosheets as Efficient Water Splitting Electrocatalysts. Adv. Energy Mater. 2015, 6, DOI: /aenm (8) Xia, C.; Jiang, Q.; Zhao, C.; Hedhili, M. N.; Alshareef, H. N. Selenide Based Electrocatalysts and Scaffolds for Water Oxidation Applications. Adv. Mater. 2015, 28, (9) Liu, X.; Chang, Z.; Luo, L.; Xu, T.; Lei, X.; Liu, J.; Sun, X. Hierarchical Zn x Co 3-x O 4 Nanoarrays with High Activity for Electrocatalytic Oxygen Evolution. Chem. Mater. 2014, 26, (10) Feng, J.; Xu, H.; Dong, Y.; Ye, S.; Tong, Y.; Li, G. FeOOH/Co/FeOOH Hybrid Nanotube Arrays as High Performance Electrocatalysts for the Oxygen Evolution Reaction. Angew. Chem. Int. Ed. 2016, 55, S-11